FIG. 1 is a diagram illustrating a configuration example of a WDM optical communication system. The WDM optical communication network illustrated in FIG. 1 includes optical nodes 1 and 1′ that are coupled with each other by a pair of WDM transmission paths 4A and 4B. A WDM light obtained by multiplexing a plurality of optical signals with various wavelengths is transmitted to and from the optical nodes 1 and 1′.
The optical node 1 includes, for example, a wavelength multiplexing device 2A, which multiplexes optical signals transmitted from a plurality of transponders 1-1, 1-2, etc., to 1-n corresponding to various wavelengths λ1 to λn and the optical signals transmitted from the transponders 1-1 to 1-n and then outputs the multiplexed optical signals to the WDM transmission path 4A, and a wavelength separating device 3B, which separates the WDM light transmitted through the WDM transmission path 4B into optical signals with the wavelengths λ1 to λn and sends the optical signals to the transponders 1-1 to 1-n corresponding to the wavelengths, respectively. The optical node 1′ includes a wavelength multiplexing device 2B, which multiplexes the optical signal transmitted from the plurality of transponders 1-1′, 1-2′, etc., 1-n′ corresponding to the wavelengths λ1 to λn and from the transponders 1-1′ to 1-n′ and outputs the optical signals to the WDM transmission path 4B, and a wavelength separating device 3A that separates the WDM lights transmitted through the WDM transmission path 4A into the optical signals with the wavelengths λ1 to λn and sends the optical signals to the transponders 1-1′ to 1-n′ corresponding to the wavelengths, respectively.
In the optical node 1, an optical packet signal SCL transmitted from the client side is sent to each of the transponders 1-1 to 1-n. In each of the transponders 1-1 to 1-n, after the optical packet signal SCL transmitted from the client side is converted into an electric signal by a light reception unit (O/E) 11, the electric signal is subjected to mapping processing by a framer 12 corresponding to a frame configuration such as Optical Transport Network (OTN). After the electric signal processed by the framer 12 is converted into an optical signal with a narrow band wavelength by a light emission unit (E/O) 13, the electric signal is transmitted to the wavelength multiplexing device 2A. The wavelength multiplexing device 2A generates a WDM light sNE by multiplexing the optical signal with the wavelengths λ1 to λn output from the E/O 13 of the transponders 1-1 to 1-n, and the WDM light sNE is transmitted to the optical node 1′ through the WDM transmission path 4A on the network side.
In the optical node 1′, the WDM light sNE transmitted through the WDM transmission path 4A is separated into the optical signals with the wavelengths λ1 to λn by the wavelength separating device 3A. The separated optical signals are sent to the transponders 1-1′ to 1-n′ corresponding to the wavelengths, respectively. In the transponders 1-1′ to 1-n′, the optical signal from the wavelength separating device 3A is converted into an electric signal by a light reception unit (O/E) 14, and the electric signal is subjected to demapping processing by the framer 12. The electric signal that is subjected to the demapping processing by the framer 12 is converted into an optical packet signal SCL with a desired wavelength by a light emission unit (E/O) 15 and is then transmitted to the client side. Between the optical node 1 and the optical node 1′, in the similar way in which the above-described transmission of the WDM light from the optical node 1 to the optical node 1′ is performed through the WDM transmission path 4A, the WDM light transmission, which is in the reverse direction from the optical node 1′ to the optical node 1, is performed through the WDM transmission path 4B.
In the WDM optical communication system as illustrated in FIG. 1, regardless of the existence of the optical packet signal SCL from the client side, the wavelength allocated to each of the transponders always occupies a channel of a WDM line on the network side. That is, corresponding to the optical packet signals SCL transmitted from the client side, a wavelength channel of the WDM light transmitted on the network side is set to be fixed. Thus, if the optical packet signal SCL from the client side is transmitted in a burst manner to each of the transponders, the transponder transmits the optical signal with a prescribed wavelength in a time in which the optical packet is received from the client side. Regarding the transmission of the WDM light on the network side, decrease of line efficiency is a problem.
As illustrated in FIG. 2, for example, as a related art, there is a network configuration in which burst transmission of the WDM optical packet signal is performed by using an Optical Packet Switch (OPS). As a Related art, for example, Japanese Laid-open Patent Publication No. 2002-261691, H. Furukawa et al., “IP over Optical Packet Switch Network with Novel 10 Gigabit-Ethernet/80 Git/s-Optical-Packet Converter” IEICE Technical Report Vol. 107, No. 108, PN2007-13, pp. 21-26, August 2007 is disclosed.
Specifically, according to the network configuration illustrated in FIG. 2, after the optical packet signal SCL transmitted to the transponder 5 from the client side is converted into an electric signal by a light reception unit (O/E) 51, the optical packet signal SCL is decomposed into a plurality of data signals by a packet decomposing circuit 52. The data signals decomposed by the packet decomposing circuit 52 are converted into light by an E/O 53 with the wavelengths λm to λm+n that are different from each other and are then sent to an optical packet multiplexing device 54. An optical label of the wavelength λk, which is obtained by converting the label signal indicating destination information and node switch information into the light by the E/O 53 and is then output from the packet decomposing circuit 52, is sent to the optical packet multiplexing device 54. The optical packet signals with the wavelength λm to λm+n and the WDM optical packet signal SNE obtained by wavelength-multiplexed with the optical label of the wavelength λk are output from the optical packet multiplexing device 54. The WDM optical packet signal SNE is time-division multiplexed with the other transponder, of which the description is omitted by a time-division multiplexing device 6A, and is then transmitted to the WDM transmission path 7A on the network side.
FIG. 3 is a diagram illustrating an example of the optical packet signal SCL from the client side and of a correspondence relation between the optical packet signals with the wavelengths λm to λm+n and the optical label of the wavelength λk. In the example illustrated in FIG. 3, the continuous data 1-1 to 1-10 and 1-11 to 1-X of the optical packet signal SCL from the client side corresponding to eight wavelengths, that is, the wavelengths λm to λm+7, and are decomposed (parallelized). In FIG. 3, a numeral L indicates an area in which the label information is stored, and a numeral E indicates an empty data area.
The WDM optical packet signal SNE transmitted through the WDM transmission path 7A is sent to an optical node switching controller 8A allocated on the WDM transmission path 7A. In the optical node switching controller 8A, some of the WDM optical packet signals SNE are branched by an optical branch unit 81 and are then sent to a label control circuit 82. In the label control circuit 82, the optical label of the wavelength λk is extracted from the branched light branched by the optical branch unit 81. Based on the node switch information included in the label signal reproduced by optical-converting the optical label, the signal COPS that controls the operation of an Optical Packet Switch (OPS) 83 coupled with a later stage of the optical branch unit 81 (see the signal waveform illustrated in the lowest stage in FIG. 3). Regarding the OPS 83, according to the control signal COPS generated by the label control circuit 82, the WDM optical packet signal SNE that passes through the optical branch unit 81 is switched to be output to the transponder 5′ side or to the WDM transmission path 7A side on the downstream.
In the transponder 5′, after the WDM optical packet signals SNE output from the optical node switching controller 8A are separated by an optical packet separating device 55 into the optical packet signals with the wavelengths λm to λm+n and the optical labels with the wavelengths λm to λm+n, and ζk, respectively, the signals are converted into electric signals by a light reception unit (O/E) 56 corresponding to the wavelengths λm to λm+n, and λk, respectively, and then converted into electric signals by the O/E 56 corresponding to the wavelengths λm to λm+n, and λk, respectively. The data signal output from the O/E 56 corresponding to the wavelengths λm to λm+n and the label signal output from the light receiver 56 corresponding to the wavelength λk are serialized by a packet assembling circuit 57 and are then converted into light by the E/O 58. After that, the optical packet signal SCL is transmitted to the client side.
Between the transponders 5 and 5′, in the similar way in which the transmission of the optical packet signal from the transponder 5 to the transponder 5′ through the WDM transmission path 7A and the optical node switching controller 8A is performed, the transmission of the optical packet signal in the reverse direction from the transponder 5′ to the transponder 5 is performed through the WDM transmission path 7B and an optical node switching controller 8B.
In this manner, the optical packet signal is generated by decomposing a single client signal into a plurality of signals and allocating the signals to various wavelengths, and the WDM optical packet signal, which is obtained by adding the optical label to the optical packet signal, is generated and transmitted to the network side. Moreover, by controlling the optical switch on the WDM network according to the optical label to switch the code, the WDM optical packet signal may be efficiently burst-transmitted.